Sorry that error is no longer showing in Xcode. I replaced the InAppBrowserBridge file I had setup manually with the prefab which seems to have fixed it.
However the browser is not opening. In the logs within Xcode I can see:
InAppBrowser: FinishedLoading https://google.com/ InAppBrowserBridge:OnBrowserFinishedLoading(String)
I expected the browser to open and work looking at the logs but I have nothing showing on screen.